The main objective of line adapters is to allow groups of transmission lines to exchange information with the Central Control Unit (CCU) of the communication controller, thus avoiding the necessity of connecting each line individually to said CCU. Therefore the line adapters include scanning means for cyclically scanning the lines. Such a line adapter has already been described in commonly-assigned, copending Patent Applications EP-A-0,048,781 and EP-077,863. In said line adapter, the transmission lines connected to the user terminals exchange information with the scanning means through line interface circuits (LICs) regrouped on a LIC unit. Each LIC unit can include up to eight LICs and is connected to the scanning means by a parallel bus and adequate connectors. These connectors have quite a large size and are accordingly space consuming in the machine and are expensive.
Thus, due to the parallel bus between the LICs and the scanning means, the connectivity of the communications controller is limited.
These drawbacks have been removed, as explained in Patent Application EP-0,232,437, by multiplexing the information exchanged with the LICs and transmitting it through a serial synchronous link implemented between the LICs and the line scanning means (called Front End Scanner FES in the cited applications) of each line adapter of the communications controllers.
Thus, due to the serial link, the LIC units and multiplexer interfaces can be, if necessary, implemented outside of the Communications Controller machine frame or at it's periphery; accordingly, the connectivity, LIC switchability and overall performances are increased.
However, the introduction of a serial link into the line adapters would normally require an important modification of the scanning means hardware and microcode. It may be far more interesting, from a technical and economical point of view, to keep the known scanning means and scanner microcode and to introduce between said scanning means and the serial link, an appropriate interface.
In the present invention the FES is the master device from which the FESA must immediately take the information presented by the FES. Similarly, when the FES requires information from a given line X, the FESA must have this information ready for it.